1. Field of the Invention
The present invention relates to a weightlifting apparatus operative to provide a continuous adjustable resistant force to a muscle-generated force produced by an exerciser that performs supination of biceps simultaneously with other exercise motions or pronation of triceps simultaneously with other exercise motions.
2. Description of the Related Art
Weightlifting apparatus for performing simultaneously two exercise motions are well known in prior art. A typical structure representative of these apparatus includes a bar with rotatably attached handles and changeable weights suspended opposite ends of the bar. The structure is configured to allow an exerciser to simultaneously perform, for example, flexing and supination of biceps or extension and pronation of triceps, wherein the supination motion is characterized by turning the palm upward, whereas the pronation motion is performed by turning the palm downward. Typically, such a structure is operative to generate a controllable force resistant only to a force generated by flexing/extending motion, but not to a torque generated by supination/pronation motion. Accordingly, muscle development controlled by the supination and/or pronation motions may be not as effective as desired.
Another type of the known weightlifting devices operative to simultaneously perform the supination/pronation exercises in combination with other exercises is operative to utilize weightlifting resistance to, for example, simultaneously perform biceps flexing biceps supination exercises. While the resistance to flexing motion is provided by using changeable weights, which can be easily selected from a very wide range to correspond to the muscle development level of the exerciser, the resistance to supination is caused by friction between the rotatable and non-rotatable parts of a handle assembly. Such a structure does not provide for an easy adjustment of resistance. Moreover, the adjustments range from near-zero to locking is very small and cannot be consistently reproduced, since there is no quantifiable indication of actual resistance. The level of resistance in such an apparatus is dependent on geometrical tolerances, the surface finishes and wears resistance of the involved parts and, therefore, may vary greatly from one apparatuses to the other or during usable life of the same apparatus. Another disadvantage of these apparatus is determined by the fact that if the motion is stopped, for example, at the point where the direction is changed from lifting to lowering the apparatus, a friction force provides no resistance to the supination motion of muscles. Also, a force resistant to a torque, which is generated during supination motion, is generated only when the exerciser lifts the apparatus, but not when the apparatus is being lowered, since during that part of the motion (to the starting position) the hands of the exerciser are exposed to pronation resistance. As a result, the intended muscles are loaded only during 50% of the exercise motion.
Still in another example of known apparatus for simultaneously performing two exercise motions, a spring-loaded supination/pronation motion unit is operative to generate a variable resistant depending whether a spring is in a contracted state or an expanded state during an exercise. However, it is a constant resistant force that is particularly beneficial the desired muscle development. In thus configured apparatus, during early stages of the lifting operation, a force created by the spring is directed through the center of rotation of both rotatable handles and totally equals to its normal component, whereas the tangential component is equal to zero. When the positions of the rotatable handle changes during the exercise, the spring force no longer passes through the center of both of the rotatable handles. During the rotational motion of the handles the normal component of the resultant force is gradually decreasing and the tangential component is increasing until the handles are rotated at 90° from the initial position. At this point the resultant force is equal to its tangential component, and the normal component is equal to zero. The resistance to be overcome by the muscles during the supination or pronation motion depends only upon the tangential component responsible for the generation of the resistant torque. Since this component constantly changes, the apparatus does not provide for constant resistance, which, as discussed above, is critical to the muscle development.
Yet another type of known apparatus for simultaneously performing two exercise motions, which utilize weightlifting resistance to multiple motions, allows performing only one or a very limited number of exercises and has a complex structure. Furthermore, the device strictly restricts the motion trajectory.
A need, therefore, exists for a weightlifting apparatus that allows the development of muscles by carrying out at least two exercise motions simultaneously under consistent, continuous and adjustable load.